Aluminum based alloys containing Sn, Pb and Cd are commonly used in bearings found in internal combustion engines. The bearing function in these alloys is performed by the soft second phase particle of the alloying element which melts in the event of lubricant failure and prevents contact between the aluminum in the alloy and the steel protected by the bearing.
In the prior art, the soft second phase in these alloys separates during solidification and often appears in the form of non uniform distribution. In many cases the second phase forms at grain boundaries as a continuous layer, or the heavier component (Sn, Pb, Cd) settles to the bottom due to gravity segregation. Typically, heat treatment is required after cold rolling of the cast sheet to redistribute the soft phase. For Al—Sn alloys for example, this is done by an annealing treatment at 662° F. (350° C.) during which the soft phase melts and coagulates into a desired uniform distribution of unconnected particles. In a final processing step, the strip is bonded on a steel backing for use as bearings in engines.
Twin roll casting of Aluminum based bearing alloys yields better distribution of the second phase particles compared to conventional ingot casting. A drawback of twin roll casting, however, is that the method is slow, yields low productivity and creates a distribution of the soft phase(s) that is not completely desirable. Suitable results are also produced using a powder metallurgy process; however this method is expensive. There is a need, therefore, for a method that results in higher productivity and yields a uniform distribution of fine particles of the soft phase in the aluminum matrix.